Advice needed on studio flash options for UVA and B

[JMC]

Another update.

 

Been a long time since I posted about this. I did place an order for some custom quartz tubes, made to the same size specification as the original Bowens GM500 ones. After being told they'd take a couple of months to produce, it eventually took about 4 months to make and get to me. Also got some Bowens suitable mounting posts, so I could use them in the same way as the original tubes, and some of the UV grade acrylic to make safety screens for the front of the flash reflectors.

 

I now have the original coated tubes, some clear uncoated glass ones (from Phoxene) and the new quartz ones (made to the same size specifications as the old ones). Once I've done some comparative tests, I'll post the results.

[dabateman]

Great,

Now that I have been able to see UVC, I have been trying to look at a portable light or flash capable of 254nm emmission. I look forward to your quartz flash test to see if you get anything that low.

 

Oddly battery powered portable 254nm fluorescent lights are quite cheap. But only use a G4T5 bulb, so 4W. But use only 4 AA batteries. Still thinking about it.

The KSS 60mm needs to be in full macro. I will need to test the UAT to see if I can get a wider field. But for some reason the focal plain in 254nm is super thin. Not sure why.

[JMC]

Initial testing results. I have 3 different flash tubes for the Bowens GM500 head;

 

Original coated tube.

Clear glass uncoated tube from Phoxene

Quartz tube from Xenon Flash Tubes

 

I worked with Xenon Flash Tubes to get quartz tubes made to the same size specification as the original Bowens tubes. Here's a comparison;

 

 

The mounting posts for the Quartz tubes came from Phoxene in France (who made the clear glass tubes I have).

 

For the test I used one tube, mounted in a Bowens GM500 head. I tested each tube. Power setting 3 (settings go from 1 to 6), cycled a couple of times before each measurement. No reflector on the flash. I took spectra from each one using my Ocean Optics FX device, setup for irradiance measurements. Cosine corrector for the collector fiber was 80cm from the flash bulbs. There was no acrylic protector in front of the tubes for this.

 

Firstly the spectra up to 850nm;

 

I've cropped the y-axis as the peaks above 800nm are huge for all the tubes.

 

Now focussing in on 450nm and below;

 

The uncoated glass tube gives out significantly more UV than the original coated tube with the UV blocking coating on it (as expected).

 

The quartz tube looks to be very similar to the clear uncoated glass one above 400nm. They are very similar down to about 350nm, but with slightly more light from the quartz one. Below 350nm, the difference gets gradually bigger, and the quartz tube gives out about 40% more than the clear glass one by the time you get down to 300nm. The quartz then carries on producing light down to 250nm and perhaps even below (although that is the limit of my devices calibration).

 

Given the way most cameras are used for UV imaging work, the majority of their sensitivity is in the 350nm to 400nm range. The quartz tube is offering little improvement there. If being used for UVB imaging (down around 300nm) then the quartz becomes more useful there, and there is even light for the UVC imaging, although not a lot. I suspect the quartz tubes will give a better range of 'colours' in our UV images too, given the increased amount of short wavelength light.

[dabateman]

Thank you,

Not as much as I was hoping for. But about 20% is not bad. I say 20% as 550nm looks to be a nice 100, and that is the typical calibration. The advantage of the flash is very short duration, but problem would need many flash bursts.

Still maybe easier to protect myself from it, than a large tube.

[Mark Jones]

https://www.dpreview.com/news/4427543600/yongnuo-yn200-speedlite-pocket-sized-flash-officially-launched

 

these 200w battery lion flashes are getting MUCH cheaper. I wonder how good the uv transmission is? the 4 pin bulbs they use are pretty common.

 

would make excellent field units.IMHO.

[dabateman]

Yes Mark I saw that last night. Similar to the Godox AD200, but $50 cheaper. Ulf I think had links for a godox quartz tube.

[Mark Jones]

https://www.xenonflashtubes.com/spiral-helical-flash-lamps/hps-6037-quartz-spiral-1500ws-flash-tube-lamp-studio_166.html

 

looks like this $128 bulb might work if modified with banna clips.

I tried to order from xenon flash tubes before off ebay, after about 2 months of waiting I cancelled my order. I also asked them to make a huge serial ring light array about a year ago, never got back to me. hopefully there service is better now. Seems like they are successful enough but have trouble managing smaller orders that get put to the side.

[SteveE]

The Yongnuo flash does not appear to have interchangeable heads like the Godox. I bought a few spare Godox bare bulb heads (without bulbs) when they were available on eBay for about $35 each, so that I could dedicate them to various xenonflashtubes bulb experiments. That way I can switch back and forth between regular photographic flash use and my various modifications quickly and easily.

[Mark Jones]

that is correct the heads are not interchangeable, but I believe the bulbs are. Otherwise one woudl have to ship the unit back to get a bulb put in? Wouldn't make sense.

[Bill De Jager]

There are two basic approaches to failure assessment and handling.

 

1. Assume there never be a failure and be unpleasantly surprised when this event is manifested. The rarer the event the more unpleasant it likely will be experienced.

 

2. Assume there will be a failure, albeit with inherent low risk, and take proactive measures to ensure the bad impact of a failure, if it occurs, is mitigated as far as possible.

 

Looking at the flash designs, the makers obviously have followed Alt.2.

 

The Bowens glass dome was only made for the Gemini 1000 and 1500 models, not for the lower-powered models. I have a 750 which uses the same tube as the 1500 but at half the power. My plan has been that I'll step out for the actual flash and that no person would be exposed to UV or glass hazard. In any case I won't be using the unit until I have a safe space to use it in.

 

JMC, thank you for the graphs!

[JMC]

No problem Bill. Should you ever need to make a protective shield, the UV sunbed grade acrylic Ulf mentioned has worked really well for me.